1. Field of the Invention
The present invention relates to a photographed (radiographed) image data acquisition method and a photographed (radiographed) image data acquisition device which are applied to so-called CT (Computerized Tomography), which involves such operations as projecting cone-shaped radiation toward the subject from different directions of projection to acquire projected image data for each of the directions of projection, and on these projected image data, generating volume data for the subject.
2. Description of the Prior Art
Nowadays, in the field of medical video engineering, there is extensive research into technology for detecting three-dimensional radiation image information, and for example, the helical CT and the cone-beam CT have been proposed (xe2x80x9cCone-Beam CTxe2x80x94Present Status and Future Prospectsxe2x80x9d Image Information (M); January, 1988, p122 to p127. Refer to Japanese Unexamined Patent Publication No. 9 (1997)-253079).
Here, the xe2x80x9ccone-beam CTxe2x80x9d is the technology with which a radiation source and a two-dimensional radiation detector are disposed so that the subject is interposed between them; the radiation source and the radiation detector are turned around the subject relative to the subject while cone-shaped radiation is projected toward the subject from the radiation source; on the basis of the permeated radiation image data (precisely speaking, the projected image data) for the subject in the different angular positions, i.e., for the directions of projection which is obtained by detecting, with the radiation detector, the radiation which permeates the subject, the volume data for the subject is acquired; on the basis of the volume data, a three-dimensional image or a tomographic image is displayed on an image display device, or a three-dimensional image or the like is once stored in a memory device. Here, xe2x80x9cthe radiation detectorxe2x80x9d refers to a detector mainly consisting of a semiconductor which detects the radiation, and converts it into an electric signal.
Incidentally, with the above-stated conventional cone-beam CT, the region where a three-dimensional image or a tomographic image can be displayed is limited to within the inscribed circle for the region provided by the overlapping portion for all the directions of projection, specifically, for the projection region for all the radiant rays which is formed by the cone-shaped radiation in each direction of projection, when the radiation detector has an area large enough to detect all the cone-shaped radiant rays. Therefore, the region where an image can be displayed is determined by the projection angle for the radiation and the detection region for the radiation detector, and if the image region is to be enlarged, it is required to project a wider angle of cone-shaped radiation (hereafter called xe2x80x9cwide-angle radiationxe2x80x9d) on the subject, and, with the detector, to detect the wide-angle radiation which permeates the subject. In other words, it is required to use a large-area detector, and project radiation having a projecting angle wide enough to cover the entire surface of the detector.
However, it is difficult to manufacture a large-area radiation detector having a large detection region, and if it could be manufactured, the manufacturing cost would be high, resulting in an expensive device. Therefore, with the conventional CT, it has been difficult to display an image of a large region.
The first photographed image data acquisition method according to the present invention is a photographed image data acquisition method with which a radiation source and a radiation detector disposed so that the subject is interposed between them are turned around the subject relative to the subject while cone-shaped radiation is projected toward the subject from the radiation source, and the radiation which permeates the subject is detected with the radiation detector to obtain photographed image data for the subject,
in which the entire detection region for each of the direction of projections is divided into a plurality of partial regions; the partial radiation detector is moved to each of these partial regions formed by the division; and
by synthesizing the photographed image data for the partial regions which is obtained by detecting, with the partial radiation detector, the radiation which permeates the subject for each of the partial regions, the photographed image data for the entire detection region is obtained.
Here, xe2x80x9cphotographed image data for the subjectxe2x80x9d means permeated radiation image data and projected image data or volume data, further, image data for output which carries a projected image, a three-dimensional image, or a tomographic image. Here, xe2x80x9coutputxe2x80x9d means outputting of image data to an image display device, a printing device, a memory device, or other device which can input image data. These definitions are also applicable hereinbelow.
xe2x80x9cBy synthesizing the photographed image data for the partial regions, the photographed image data for the entire detection region is obtainedxe2x80x9d refers to any processing which synthesizes the permeated radiation image data or the like for the partial regions to obtain the permeated radiation image data or the like for the entire detection region. For example, it refers to obtaining volume data for the entire detection region on the basis of the projected image data for the partial regions, obtaining image data for output carrying a tomographic image for the entire detection region on the basis of the volume data for the partial regions, or the like, as well as synthesizing the permeated radiation image data for the partial regions to obtain the permeated radiation image data for the entire detection region, synthesizing the projected image data for the partial regions to obtain the projected image data for the entire detection region or synthesizing the volume data for the partial regions to obtain the volume data for the entire detection region.
In moving the partial radiation detector to each of the partial regions formed by the division, it is moved so that each of the partial regions formed by the division is completely covered by the detection region, in other words, the detection region covers each of the partial regions. In this way, for each of the directions of projection, the partial radiation detector is moved in increments of the specified distance corresponding to the above-mentioned division, and in each of the changed-over photographing positions, the photographed image data for the partial regions which is obtained by detecting, with the partial radiation detector, the radiation which permeates the subject is synthesized to obtain the photographed image data for the entire detection region. The number of partial radiation detectors may be one or more than one.
With this first photographed image data acquiring method, it is, of course, preferable to make the above-mentioned division so that the plurality of partial regions are consecutive. In other words, it is preferable that the above-mentioned specified distance in increments of which the partial radiation detector is to be moved be such that the adjacent detection regions for the radiation detector in each of the photographing positions overlap each other.
The second photographed image data acquiring method according to the present invention is a photographed image data acquiring method with which a radiation source and a radiation detector disposed so that the subject is interposed between them are turned around the subject relative to the subject while cone-shaped radiation is projected toward the subject from the radiation source, and the radiation which permeates the subject is detected with the radiation detector to obtain photographed image data for the subject,
in which a plurality of partial radiation detectors disposed in such an arrangement that the entire detection region is covered constitute the radiation detector; and
by synthesizing the photographed image data which is obtained by detecting, with the plurality of partial radiation detectors, the radiation which permeates the subject, the photographed image data for the entire detection region is obtained.
Here, xe2x80x9cBy synthesizing the photographed image data which is obtained by detecting, with the plurality of partial radiation detectors, the radiation which permeates the subject, the photographed image data for the entire detection region is obtainedxe2x80x9d refers to any processing which synthesizes the permeated radiation image data or the like obtained by detecting, with the plurality of partial radiation detectors, the radiation which permeates the subject to obtain the permeated radiation image data or the like for the entire detection region. For example, it refers to obtaining volume data for the entire detection region on the basis of the projected image data, obtaining image data for output carrying a tomographic image for the entire detection region on the basis of the volume data for the partial regions, or the like, as well as synthesizing the permeated radiation image data to obtain the permeated radiation image data for the entire detection region, synthesizing the projected image data to obtain the projected image data for the entire detection region or synthesizing the volume data to obtain the volume data for the entire detection region.
With this second photographed image data acquiring method, it is preferable to dispose the plurality of partial radiation detectors so that the adjacent detection regions overlap each other.
The first photographed image data acquiring device according to the present invention is a photographed image data acquiring device which realizes the above-stated first photographed image data acquiring method, i.e., a photographed image data acquiring device which is equipped with a radiation source and a radiation detector disposed so that the subject is interposed between them; and turns the radiation source and the radiation detector around the subject relative to the subject while projecting cone-shaped radiation toward the subject from the radiation source, detecting the radiation which permeates the subject with the radiation detector to obtain photographed image data for the subject, comprising:
a partial radiation detector;
mover means which moves the partial radiation detector to each of a plurality of partial regions formed by dividing the entire detection region for each of the directions of projection; and
photographed image data synthesizer means which, by synthesizing the photographed image data for the partial regions obtained by detecting, with the partial radiation detector, the radiation that permeates the subject for each of the partial regions to which the partial radiation detector is moved, provides the photographed image data for the entire detection region.
In moving the radiation detector to each of the partial regions formed by the division, it is preferable to move the radiation detector so that each of the partial regions formed by the division is covered by the detection region. In other words, it is preferable that the above-mentioned moving means move the partial radiation detector in increments of the specified distance corresponding to the above-mentioned division for each of the directions of projection. Further, it is preferable that the division be made so that the plurality of partial regions are consecutive, in other words, the above-mentioned movement is made in increments of the distance which causes the adjacent detection regions for the partial radiation detector to overlap each other in each of the photographing positions.
The second photographed image data acquiring device according to the present invention is a photographed image data acquiring device which realizes the above-stated second photographed image data acquiring method, i.e., a photographed image data acquiring device which is equipped with a radiation source and a radiation detector disposed so that the subject is interposed between them; and turns the radiation source and the radiation detector around the subject relative to the subject while projecting cone-shaped radiation toward the subject from the radiation source, detecting the radiation which permeates the subject with the radiation detector to obtain photographed image data for the subject,
in which the radiation detector comprises a plurality of partial radiation detectors disposed in such an arrangement that the entire detection region is covered; and
comprising photographed image data synthesizer means which, by synthesizing the photographed image data obtained by detecting, with each of the plurality of partial radiation detectors, the radiation that permeates the subject, provides the photographed image data for the entire detection region.
It is preferable that the plurality of partial radiation detectors for this second photographed image data acquiring device be disposed so that the adjacent detection regions overlap each other.
With the first photographed image data acquiring method and the first photographed image data acquiring device according to the present invention, the entire detection region for each of the directions of projection is divided into a plurality of partial regions; the partial radiation detector is moved to each of these partial regions formed by the division; and by synthesizing the photographed image data for the partial regions which is obtained by detecting, with the partial radiation detector, the radiation that permeates the subject for each of the partial regions to which the partial radiation detector is moved, the photographed image data for the entire detection region is obtained. Therefore, on the basis of the permeated radiation image data or the projected image data for the entire detection region which is synthesized, the volume data for the entire detection region can be generated or the volume data for the entire detection region can be synthesized, and thus, without using a large-area radiation detector, a three-dimensional image or a tomographic image of a region larger than the photographing capable region which is defined by the detection region for the small-area detector can be formed for display output or other purpose. If the division is made so that the plurality of partial regions are consecutive, no regions where the acquired photographing image data is not detected are produced, and thus a smooth image having no seams can be obtained.
On the other hand, with the second photographed image data acquiring method and the second photographed image data acquiring device according to the present invention, the radiation detector is constituted by a plurality of partial radiation detectors disposed in such an arrangement that the entire detection region is covered, and by synthesizing the photographed image data obtained by detecting, with each of the plurality of partial radiation detectors, the radiation that permeates the subject, the photographed image data for the entire detection region is obtained. Therefore, as is the case with the first photographed image data acquiring method and the first photographed image data acquiring device, on the basis of the permeated radiation image data or the projected image data for the entire detection region which is synthesized, the volume data for the entire detection region can be generated or the volume data for the entire detection region can be synthesized, and thus, without using a large-area radiation detector, a three-dimensional image or a tomographic image of a region larger than the photographing capable region which is defined by the detection region for the small-area detector can be formed for display output or other purpose.
If the plurality of partial radiation detectors are disposed so that the adjacent detection regions overlap each other, no regions where the acquired photographing image data is not detected are produced, and thus a smooth image having no seams can be obtained.
The purpose of the present invention is to offer a photographed image data acquiring method and a photographed image data acquiring device for cone-beam CT which is capable of providing such a function as displaying an image of a region larger than the photographing capable region defined by the detection region without using a large-area radiation detector.